In the above technical field, patent literatures 1 and 2 disclose techniques of obtaining the distance to a target based on the frequency difference between a transmitted chirp wave and a chirp wave reflected from the target. Furthermore, patent literature 3 and non-patent literatures 1 and 2 disclose techniques in which a dual-sweep signal that sweeps a frequency band twice the frequency band of a transmitted chirp wave in two cycles of the transmitted chirp wave is used as a heterodyne signal, and the reception wave signal of a chirp wave reflected from a target is multiplied by the heterodyne signal, thereby generating a beat frequency as the frequency difference between the heterodyne signal and the reception wave signal by performing heterodyne processing once regardless of a delay in the reception wave signal of the chirp wave.